Prior art panel benders are known which operate the process for bending a sheet of sheet metal using a pair of blades mounted on a blade holder unit which is a substantially “C” shaped structure and which may be hydraulically or electro-mechanically operated.
In this type of machine, a sheet metal sheet to be bent is clamped by a device, known as a presser or sheet presser, which moves in a direction at right angles to the plane of the metal sheet itself and is compressed against a fixed part, known as the counterblade.
Each of the two blades, upper and lower, describes a curvilinear trajectory in the two degrees of horizontal (X) and vertical (Y) freedom, in directions respectively parallel to and at right angles to the plane of the metal sheet.
During this movement the blade enters into contact with the metal sheet and bends it into various shapes. The trajectory may be fixed or in some cases is programmed on computer numeric control (CNC) systems which interpolate the two axes X and Y.
The European patent EP-B1-1819457 represents the state of the art which is closest to the present invention. Its blade holder unit has a kinematic chain which has an architecture substantially comprising a jointed pentalateral assembly whose actuating components are cranks driven by an electric motor coupled to a high-precision reduction gear suitable for high torques.
In this case the blade holder unit uses a jointed mechanism formed by two mechanical units designed to control respectively the horizontal movement and the vertical movement of the blade holder unit.
More specifically, the first mechanical unit, which controls the horizontal movement of the blade holder unit, comprises an independent servomotor fitted with a crank which is in turn connected to a connecting rod. The other end of the connecting rod hinges on the end of a lever fitted with a pivot positioned on the shaft. The other end of this lever, the end opposite the one attached to the connecting rod, is connected to a set of pins located on the ends of a pair of supports which in turn have an expanding shape linked with the blade holder.
The second mechanical unit, which controls the vertical movement of the blade holder unit, comprises two servomotors which actuate cranks which in turn are hinged on respective connecting rods. The other ends of the connecting rods are attached to the base of the “C” shaped blade holder unit.
It should be noted that all the cranks described in this patent can also be eccentric elements with the same function.
The reader can refer to the patent EP-B1-1819457 for further constructional details. It should be noted that the geometry of the mechanism described in the patent EP-B1-1819457 has the work space necessary for the correct moving of the bending blades in the fields of application of the invention. It also has the special geometrical configurations, (for the single kinematic conditions where there is kinematic inversion of motion) around the configurations where the mechanism bends the sheet of metal, needed to generate the necessary amplification of the drive torques.
The machine according to the patent EP-B1-1819457 has several major advantages in comparison with the panel bender machines of the prior art. In particular, this machine provides a new bending trajectory which allows the bending blade to roll on the metal sheet without scraping it. This trajectory is particularly useful when processing material with a protective film because it prevents breakage of the film and damage to the metal sheet.
An additional advantage is that the servomotors and reduction gear used make it possible to achieve performance levels which are certainly much higher than those obtained using the prior art hydraulic systems. The servomotors and reduction gear also guarantee the delivery of a constant torque throughout the bending cycle. This cannot be obtained with hydraulic systems which use accumulators and which therefore operate at a pressure which slowly decreases during bending. This enables consumption to be optimised and reduced to levels which are 60% lower than those of traditional machines.
A further advantage is that the semi-finished material processed with the machine made according to patent EP-B1-1819457 is of excellent quality and obtained with a machine which is considerably more stable and repeatable in comparison with traditional machines. This is because it is not sensitive to the thermal variations which occur on machines with hydraulic systems. It is also quieter than prior art machines and uses a much reduced amount of oil because it has a very simple hydraulic circuit.
The environmental impact of this machine is also completely different from that of prior art machines. It is more reliable, consumes less, is quieter and uses much less oil.
The machine described in patent EP-B1-1819457 has all the advantages described above in relation to prior art machines. However, actual use of this machine has highlighted some shortcomings and problems which do not appear to be easy to overcome. On the machine described in document EP-B1-1819457 the horizontal movement is generated by a single servomotor reducer. This feature means that the machine cannot perform off-centre bendings. In other words, with this machine it is not possible to position the metal sheet at any point in the work zone.
An additional disadvantage is that it is not possible to obtain variable bends on workpieces such as ferrules because this machine does not enable different trajectories.
Lastly, the configuration of the machine described in patent EP-B1-1819457 cannot be changed freely as required. This makes it sensitive to variations in thermal and mechanical conditions and consequently creates not inconsiderable problems in maintaining the mechanical tolerances specified.